1. Field of the Invention
This invention relates to a constant current source circuit, and more particularly, to a semiconductor current source circuit having constant current characteristics whose current level is substantially unaffected by a change in the source voltage which biases the circuit.
2. Description of the Prior Art
Constant current source circuits are often used in integrated circuit (IC) design, and many forms of these circuits have been developed. A requirement for constant current sources is that the operating current does not change when a variation in the power source voltage occurs. Constant current source circuits are also ideally required to operate at a low power supply voltage with low power consumption.
In practice, certain of the constant current source circuits used in integrated circuits have low power consumption but fail to achieve good constant current characteristics. Alternatively, other constant current source circuits are able to maintain a constant current level but are found to be less efficient insofar as power consumption is concerned.
Two types of conventional constant current source circuits are shown in FIGS. 1 and 2 and are more fully discussed below in the section entitled "Description of the Preferred Embodiments".